I'm just gonna say this, I don't get STALKER's story. I mean, it takes place is Chernobyl or Pripyat, but... I don't 100% get it. But I fucking love playing it. Dying in STALKER is your fault most of the the time. It's mostly you do something stupid in thinking that it's like a normal action name. The game is quick in saying this, in the harshest way possible. You're like "Oh hey, this is gonna be a good action game." then stalker goes "No it's not. There's more." then probably punches you in the face. It's fun, I enjoy it. I like shooting my own nationality in games. You're a Russian shooting other Russians.
Fallout 4 is basically STALKER in America during the retro-future 50s, its a FPS focusing more on exploration and gunfights with the primary means of upgrading being through use of special items like clothes and bobbleheads (artifacts) with a excellent perk system that will probably be better to what their aiming for. I just hope there will be mods that add back in the more RPGy elements.
Plus there's, like, civilization building stuff.
The story, outside of the first game, is complete rubbish. The first game is slightly less rubbish. STALKER is fun because of the environment. The Zone has history, and weird shit happens.